Cosmology with the New Generation of Cherenkov Telescopes

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Cosmology with the New Generation of Cherenkov
Telescopes
Oscar Blanch Bigas IFAE, UAB Seminari
IEEC 15-XII-04
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Introduction
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INTRODUCTION
?-ray Astronomy

• Cosmic Rays hit the Earths atmosphere (?1000 m-2
  s-1)
• What are their sources?
• What is their chemical composition?
• What are the astrophysical process of the
  acceleration?
• How do they propagate through galactic and
  extragalactic space?
• more than 99 are charged particles
• but they loose original direction
• CGRO Whipple ? breakthrough on ?-ray astronomy
  (?0.1).
• Production processes of ?-ray might also be
  responsible for the production of the CR
• Light on Fundamental Physics dark matter,
  antimatter, quantum gravity, cosmology, ...

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INTRODUCTION
Cosmology

• Cosmological Principle homogeneous and
  isotropic universe.

• In the context of general relativity, the
  dynamics of the universe is governed by the
  Friedmann equation.

Where the redshift (z) is defined as 1z ? R0 /
R(t) and therefore redshift and time are related
by the lookback-time.
Time (distance) vs redshift measures cosmology
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The Cherenkov Telescopes
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The Cherenkov Telescopes
New Generation of Cherenkov Telescopes

• Previous Situation
• Energy gap between satellites (lt10 GeV) and
  ground-based Telescopes (gt300 GeV).
• Extinction of number of sources in this gap
• For extragalactic sources ? absorption due to
  Extragalactic Background Light (EBL).

Ground-based gt 300 GeV
Satellites lt 10 GeV
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The Cherenkov Telescopes
The Big four
MAGIC (2004)
VERITAS
Roque de los Muchachos, Canary Islands
Montosa Canyon, Arizona
HESS (2003)
CANGAROO III
Windhoek, Namibia
Woomera, Australia
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The Cherenkov Telescopes
Image Air ?erenkov Technique

• IACT do not see the ?-ray hitting the atmosphere
  but the ?erenkov light from the electro-magnetic
  shower developed in the atmosphere (calorimeter
  with atmosphere as active material)

The light is collected and focused on the camera
forming and image of the electro-magnetic
shower. The image may come from a pure
electro-magnetic shower (?,e-) or from the
electro-magnetic part of hadron showers
(p,He,). Fast ?-pulse allow to reduce
background due to LONS
Altitude (Km)
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The Cherenkov Telescopes

• The images formed by hadronic showers
  (background) and electro-magnetic (signal) are
  different.

Photons point to the center!
Protons do not!
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The Cherenkov Telescopes
Moreover, the shape is also different and it is
usually described by Hillas Parameters (width,
length, dist, alpha, ...) They depend on energy
of incident ?? spectrum from each source.
?s appear
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The MAGIC Telescope
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The MAGIC Telescope

• MAGIC requests
• Lowering as much as possible the Energy
  Threshold.
• Maximum feasible sensitivity in the unexplored
  energy range.
• Extragalactic sources ? North Hemisphere.
• Fast repositioning for GRB follow-ups ? Light
  Telescope.

17 m diameter Image Air Cerenkov
Telescope _at_ Roque de los Muchachos
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The MAGIC Telescope
A second Generation IACT - MAGIC

• An advanced 17 m Telescope based on a series of
  innovative features.

17m Ø mirror Ultralight alluminum panels
85-90 reflectivity
3.5 FOV camera 577 pixels Optical fiber
analogic transmission 2 level trigger 300
MHz FADC
Light carbon fiber tubes 65 ton total
weight Frame corrected using Active Mirror Control
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The MAGIC Telescope
The Frame
The largest telescope mirror ever built by Human
Being 240 m² surface. Light weight carbon fiber
structure. 17 tons Dish Mirrors 64 tons
Telescope (fast positioning over 180? in 22s)
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The MAGIC Telescope
The Reflector

• Tessellated reflector
• 950 mirror elements
• 49.5 x 49.5 cm2
• All-aluminum, quartz coated, diamond milled,
  internal heating
• gt85 reflectivity in 300-650nm

Active mirror control Use lasers to recall panel
positions when telescope moves
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The MAGIC Telescope
Camera and signal transmission
577 PMTs Coating Double crossing Inner zone
396 pixels of 0.1? Outer zone 180 pixels of 0.2?
Optical analogic transmitters 160 m of fibres
short signal, optically decoupled, cable
weigth,...
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The MAGIC Telescope
Solarium
Bed-room
Kitchen
W C
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The MAGIC Telescope
Signal Processing

• Optical transmission over 162 m
• 1st Level Trigger 2,3,4,5-fold next neighbour
• 2nd Level freely programmable
• 300 MHz, 8 Bit FADC.
• Dynamic range 2000.
• DAQ Continuous 700 Hz

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The MAGIC Physics
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The MAGIC Physics
Dark Matter
AGNs
SNRs
g-RH Cosmology
Quantum Gravity effects
Pulsars
GRBs
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The MAGIC Physics
Active Galactic Nuclei

• Active Galactic Nuclei refers to galaxies with a
  central region where high-energetic processes
  take place.

• AGN have been found in all wavelength and they
  showed emission up to TeV energies.
• Emission in jet produced by electron or proton
  primaries?
• Highest variability in X-ray and ?-ray.
• High energy ?-ray from very far distances
  Cosmology, Quantum Gravity, ...

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Optical Depth Gamma Ray Horizon
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Optical Depth Gamma Ray Horizon
Optical Depth and GRH
Concept - EBL absorption
High energy ?-rays travelling cosmological
distances are expected to be absorbed through
their interactions with the EBL by
The integration over the path travelled across
the universe, which depends on the source
redshift (z), is the Optical Depth.
Then the ?-ray flux is attenuated while
travelling from the emission point to the
detection point.
The group of pairs (E,z) for which
is defined as the Gamma Ray Horizon (GRH)
(Fazio-Stecker relation).
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Optical Depth Gamma Ray Horizon
GRH for a specific scenario
Opaque region
GRH energy
Transparent region
source
For each source (fixed redshift) the GRH energy
(E0) is defined as the energy on the GRH.
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Optical Depth Gamma Ray Horizon
Influence of the Cosmological Parameters
look-back time

• The Hubble constant H072?4 Km s-1 Mpc-1
  (Spergel et al, 2003)

Similar shift (10 at 3?Ho) over the whole
redshift range
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Optical Depth Gamma Ray Horizon

• The cosmological densities
• ?m0.29?0.07, ??0.72?0.09 (Wang et al, 2003)

m
?
0 variation at z0 10 and 5 at z4
astro-ph-0107582 submited APh
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Optical Depth Gamma Ray Horizon
MAGIC capability

• We assume an EBL model (Kneiske et al, 2004) and
  universe with H072 Km s-1 Mpc-1 , ?m0.29 and
  ??0.72.
• MAGIC characteristics from MC Trigger
  Collection Area, Energy Threshold and Energy
  Resolution.
• The suitable ?-ray candidates
• Well known TeV emitters (Mkn421, Mkn501
  E1426428)
• Egret Sources extrapolation
• Flux extrapolation (source model data, Optical
  Depth, Culmination angle, MAGIC, 50h) ? Fit to

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Optical Depth Gamma Ray Horizon
Despite simplification, reasonable ?2 and ? Eo
1-5sta ? 1-5sys
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Cosmological Measurements
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Cosmological Measurements
The new method
The GRH energy depends on the Cosmology and the
distance to the source ? A cosmological dependent
distance estimator, which does not rely on
standard candles.
Moreover, the GRH behaves differently as a
function of redshift than other observables
already used for cosmology measurements.
The GRH can be used as an independent method to
measure cosmological parameters
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Cosmological Measurements
?m0.29, ??0.72
Four parameters fit based on a multi-dimensional
interpolating routine.
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Cosmological Measurements
Statistic Precision for ?m ??
An external constraint of 72?4 km/ s Mpc (Spergel
et al, 2003) for the Hubble constant is used.
Expected contour of 68 , 95 and
99 confidence level
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Cosmological Measurements
Estimation of foreseen systematic errors

• Systematic error on GRH determination
• Global energy scale 15
• Extragalactic Background Light

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Cosmological Measurements
Estimation of foreseen systematic errors

• Systematic error on GRH determination
• Global energy scale 15
• Extragalactic Background Light

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Cosmological Measurements

• Above redshift z?0.1, the difference on the GRH
  come from UV background.
• Fit only source with z gt 0.1
• Add one parameter to fit UV background level.

High Correlation UV-?m ? External
Constraints 5,15,25,30 (50 , Scott et al,
2000)
astro-ph-0406061 submited APh
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Cosmological Measurements
Comparison to current ?m and ?? measurements
galaxy counting, Supernovae and Microwave.
15 UV constraint
30 UV constraint
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Conclusions
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Conclusions-Outlook

• Precise Measurement of the GRH lead to a new
  technique to measure ?m and ??
• Independent from other techniques currently used.
• No standard-candle ( but uniform and isotropic
  EBL )
• Active Galactic Nuclei ? highest observable
  redshift
• The precision of this technique is dominated by
  the systematic due to the poor knowledge of the
  EBL. At least a 15-25 precision on the UV
  background level is needed (currently ?50).
• MAGIC (as well as other Cherenkov Telescopes)
  already started to observe AGNs at large redshift
  (zgt0.1).
• How many are going to be seen?
• AGN are interesting by itself but any spectrum
  from an AGN will help to get cosmological
  information with this method.